1. Field of the Invention
The invention relates generally to methods for making capillary splices. More specifically, the invention relates to a method for making glass tubing.
2. Background Art
Fiber-optic systems require means for transferring energy from one optical fiber to another without undue power loss. One means for transferring energy from one optical fiber to another is to position the optical fibers in an end-to-end relationship so that light emanating from one fiber end face is directed into the adjacent fiber end face.
Capillary splices (also known as ferrules) are used to align sets of optical fibers in an end-to-end relationship. FIG. 1 shows a cross-section of a prior-art capillary splice 1, which includes a tubing 2 having a longitudinal bore 3. The tubing 2 may be made of ceramic, glass, glass-ceramic, or polymeric material. In general, the tubing material will depend on the anticipated application requirements. Terminal ends of optical fibers 4, 5 are inserted into the bore 3 to place the optical fibers 4, 5 in an end-to-end relationship.
It is usually desirable to make the diameter of the bore 3 only a few microns larger than the diameter of the optical fibers 4, 5 so that the optical axes of the optical fibers 4, 5 remain substantially aligned when inserted into the bore 3. Funnel-like apertures 6, 7 are typically formed at the ends of the bore 3 to facilitate insertion of the optical fibers 4, 5 into the bore 3. The funnel-like apertures 6, 7 also provide a mounting location for bonding material 8, 9, which is used to secure the optical fibers 4, 5 to the tubing 2. In general, one or both ends of the bore 3 may be terminated with a funnel-like aperture.
U.S. Pat. Nos. 4,822,389 and 4,917,718, both issued to Berkey, disclose a method for making a capillary splice from glass tubing. The method involves placing the bore of the glass tubing under pressure by filling the bore with a fluid, such as air, nitrogen, and the like, and then applying localized heat to the glass tubing. As the glass tubing is heated to its softening point, the inside wall of the bore starts to expand within the softened area by the pressure of the fluid within the bore. The pressure causes a bubble to begin to form within the glass tubing.
FIG. 2A shows a bubble 10 forming within a glass tubing 11 as the bore 12 of the glass tubing 11 is pressurized with fluid 13 and the glass tubing 11 is heated to its softening point by a burner 14. The glass tubing 11 is rotated as it is heated to allow for uniform heat distribution along the diameter of the glass tubing 11. As the glass tubing 11 is rotated and subjected to localized heating, the bubble 10 continues to expand until it occupies a major portion of the diameter of the glass tubing 11. FIG. 2B shows the bubble 10 occupying a major portion of the diameter of the glass tubing 11. The outer diameter of the glass tubing 11 in the vicinity of the bubble 10 may increase slightly as a result of the bubble growth within the glass tubing 11. This slight increase in diameter may be eliminated by stretching the glass tubing 11 along its longitudinal axis as the bubble 10 is formed.
Multiple bubbles can be formed at spaced intervals along the length of the glass tubing 11 using the process described above. FIG. 2C shows two bubbles 10 formed within the glass tubing 11 using the process described above. To form the splice, the glass tubing 11 is scored along its exterior surface at about the center of each of the bubbles 10. Thereafter, the glass tubing 11 is severed along the score line to produce the splice.
As previously mentioned, splices are used to align and couple optical fibers. Therefore, they must be manufactured with extreme precision and tight tolerances to avoid undue power loss between the optical fibers. The process of forming a capillary splice that meets required specifications starts with a glass tubing having precise inner and outer dimensions.
In one aspect, the invention relates to a method of making glass tubing which comprises assembling together a first glass rod having at least one bore and a second glass rod having at least one bore into a single glass unit, shaping an outer surface of the glass unit to a desired cross-section, and drawing the glass unit to form a glass tubing having a predetermined inner and outer dimension.
In another aspect, the invention relates to a method of making glass tubing which comprises assembling together a first glass rod having at least one bore and a second glass rod having at least one bore to form a single glass unit, shaping an outer surface of the glass unit to a desired cross-section, inserting the glass unit into an outer clad glass tube to form a tube assembly, and drawing the tube assembly to form a glass tubing having a predetermined inner and outer dimension.
Other features and advantages of the invention will be apparent from the following description and the appended claims.